I. Field of the Invention
The present invention relates to fuel pumps and, more particularly, to a high pressure fuel pump for use with a direct injection internal combustion engine.
II. Description of Related Art
Direct injection internal combustion engines are enjoying increased popularity, particularly in the automotive industry. In a direct injection internal combustion engine, the fuel is injected directly into the internal combustion chamber. Such direct injection engines enjoy increased engine efficiency, fuel economy, and reduced emissions.
Since the fuel is injected directly into the internal combustion chamber in a direct injection engine, the fuel supply to the fuel injectors must necessarily be provided at a high pressure. In order to accomplish this, a high pressure fuel pump provides high pressure fuel to fuel rails which are, in turn, fluidly connected to the fuel injectors for the engine.
With reference first to FIG. 1, a typical prior art fuel pump 20 for a direct injection engine is shown. This fuel pump 20 includes a housing 22 which defines an internal pump chamber 24 having an outlet port 26. The outlet port 26 is connected to a fuel rail (not shown) through a one-way valve 28.
Still referring to FIG. 1, the housing 22 includes a fuel inlet passageway 30 which is fluidly connected to a source of fuel. This fuel inlet passageway 30 is fluidly connected to the pump chamber 24 through a port 32 formed in the housing 22.
In order to pump fuel from the pump chamber 24 out through the outlet port 26, a piston 34 has one end positioned within the pump chamber 24 and is reciprocally driven by the camshaft of the engine. Consequently, as the piston 34 moves into the pump chamber 24, the piston 34 pressurizes the fuel in the pump chamber 24 thus forcing the fuel out through the outlet port 26 and to the fuel rail assuming that the inlet port 32 is closed. Conversely, as the piston 34 moves outwardly from the pump chamber 24, the piston 34 inducts fuel through the inlet passage 30 and inlet port 32, assuming that it is open, and into the pump chamber 24.
A valve 36 is axially slidably mounted within the housing 22 and this valve 36 includes an enlarged diameter valve head 38 which overlies the inlet port 32 to the pump chamber 24. When the valve 36 is extended so that the valve head 38 is spaced apart from the port 32, the flow of fuel from the inlet passageway 30 and to the pump chamber 24 can occur through the inlet port 32. Conversely, with the valve head 38 abutting against the port 32, the valve head 38 closes the inlet port 32 so that fuel is pumped out through the outlet port 26 as the piston 34 moves into the pump chamber 24.
In order to control the movement of the valve 36 between its open and closed position, a spring 40 urges the valve 36 towards its closed position while a solenoid 42, when activated, holds the valve 36 in an open position. Consequently, upon deactivation of the solenoid 42, the spring 40 returns the valve to its closed position thus terminating fluid flow through the inlet port 32.
In operation, the movement of the piston 34 out from the pump chamber 24 creates a suction which moves the valve 36 to an open position. Once open, the actuation of the solenoid 42 maintains the valve 36 in its open position thus allowing fuel flow from the inlet passageway 30 into the pump chamber 24. As the piston 34 begins to move back into the pump chamber 24, deactivation of the solenoid 42 allows the spring 40 to return the valve 36 to its closed position so that the pressurized fuel in the pump chamber 24 flows out through the outlet port 26 as desired.
While the previously known fuel pumps for direct injection engines have proven adequate in supplying sufficient high pressure fuel to the fuel rails for the engine, the fuel pump creates an undesirable high level of noise for automotive uses. Most of this noise, furthermore, is attributable to contact or impact between the valve 36 and the pump housing 22 as the valve 36 reciprocates between its open and its closed position. This contact occurs not only between the valve head 38 and the valve seat 39 forming the inlet port 32, but also between an anchor 44 of the valve 36 and the pump housing.